Growers question fungicide use in dryland peanut crop

With the advent of disease-resistant peanut varieties, many producers are questioning the need for costly fungicide inputs, especially for controlling white mold on these new lines.

Fungicides make up a sizable portion of the variable costs in an Alabama peanut production budget, says Austin Hagan, Auburn University Extension plant pathologist. And, within the past six years, the use of fungicides for controlling white mold and rhizoctonia limb rot have added to production costs, he says.

The fungicides Folicur 3.6F, Abound 2SC and Moncut 50W are applied annually to nearly 60 percent of Alabama's peanut acreage, notes Hagan. “Although these fungicides control white mold and limb rot as well as boost the yield of irrigated peanuts, little information is available concerning their effectiveness against white mold and limb rot on dryland peanuts.

“In addition, reliable information concerning the potential yield gains obtained by controlling these and other diseases on peanuts is not available,” he says.

In the past five years, tomato spotted wilt virus (TSWV) has changed the face of peanut production throughout the Southeast, says Hagan. The once-popular Florunner and GK-7 peanuts have been forced out by TSWV and have been replaced by the virus-resistant cultivars Georgia Green, FL MDR 98, ViruGard and C-99R.

“With the exception of ViruGard, all of these peanuts — which are partially resistant to white mold and, in several cases, early and late leafspot — are called ‘multiple disease-resistant’ cultivars. And questions have been raised by farmers about the need for costly fungicide applications, particularly for controlling white mold on disease-resistant cultivars,” says Hagan.

At two locations over a three-year period, Alabama Agricultural Experiment Station researchers evaluated fungicide programs that included Folicur, Abound and Moncut applied according to label directions on selected multiple disease-resistant peanut varieties.

On the Georgia Green and Southern Runner varieties at both test sites, the Folicur and Abound programs generally reduced white mold and limb rot damage while boosting pod yields by 550 to 1,400 pounds per acre as compared with the Bravo Ultrex standard.

When the disease and yield data was pooled in each year across the white mold-susceptible and resistant cultivars, white mold and limb rot damage was reduced and pod yields typically were increased by the recommended Folicur, Abound and Moncut programs.

Peanuts in the trials were planted at a rate of approximately six seed per row foot during the first or second week of May 1997, 1998 and 1999 at the Wiregrass Research and Extension Center (WREC) in Headland, in south Alabama. In 1998 and 1999, similar peanut trials were established at the Gulf Coast Research and Extension Center (GCREC) in Fairhope in an area with a history of soybean production.

At WREC, Georgia Green and Southern Runner were sown in all three years. GK 7, which was produced in 1997 and 1998, was replaced with ViruGard and FL MDR 98 in 1999. In 1998 and 1999, the cultivars planted at GCREC were the same as those used in the corresponding year at the Wiregrass Center. Trials located at both units were not irrigated.

The rates, numbers and timing of Folicur, Abound, Moncut and Bravo Ultrex applications were according to label directions. Typically, seven broadcast applications were made at a spray volume of 15 gallons per acre at approximately 14-day intervals, beginning in early June and ending in the middle of September.

When the disease and yield data is pooled across cultivars, some differences and similarities in the performance of the fungicide programs at the two locations are seen. At WREC, a substantial reduction in leafspot levels was obtained with Folicur and Abound only in 1997.

Due to unseasonably dry weather patterns in the summer of 1998 and 1999, the Folicur and Abound programs did not give better leafspot control than did the Bravo Ultrex or Bravo Ultrex-plus-Moncut programs. In the first two years, the numbers of white mold hits were lower with the Folicur and particularly Abound programs as compared with the Bravo Ultrex standard.

As was the case with leafspot diseases, no substantial differences in white mold control were noted among the recommended fungicide programs. Despite dry late-summer rainfall patterns seen in two of three years, yield of the Folicur and Abound-treated peanuts were approximately 400 to 850 pounds per acre above those recorded for the Bravo Ultrex standard or Bravo-plus-Moncut programs.

Although some year-to-year variation in yield gains was noted with the Folicur and Abound programs, both programs - over the three-year test period — proved almost equally effective in boosting peanut yields.

“In a dryland peanut production system, control of white mold and limb rot was improved and yields substantially increased at both Headland and Fairhope on Georgia Green and Southern Runner with Folicur and Abound,” says Hagan.